John Lewis, the civil rights warrior who marched with Martin Luther King Jr and was nearly killed in police beatings before serving for decades as a US congressman, died late Friday aged 80.

The African-American icon spent his life getting into what he liked to call "good trouble" -- the confrontations necessary to improve American democracy by ending discrimination and racial injustice. 

"Today, America mourns the loss of one of the greatest heroes of American history," House Speaker Nancy Pelosi said of the 17-term congressman from Georgia.

She described Lewis, who in late 2019 was diagnosed with pancreatic cancer, as "a titan of the civil rights movement whose goodness, faith and bravery transformed our nation."

The son of sharecroppers, Lewis was just 21 when he became a founding member of the Freedom Riders, who fought segregation of the US transportation system in the early 1960s, eventually becoming one of the nation's most powerful voices for justice and equality.

He was the youngest leader of the 1963 March on Washington, in which King delivered his famous "I have a dream" speech.

Two years later Lewis nearly died while leading hundreds of marchers across the Edmund Pettus Bridge in Selma, Alabama on a peace march to Montgomery when state troopers, seeking to intimidate those demonstrating for voting rights for black Americans, attacked protesters.

Lewis suffered a fractured skull on the day that would become known as "Bloody Sunday." Fifty years later in 2015, he walked across the bridge arm in arm with Barack Obama, the nation's first black president, to mark the anniversary of the Selma to Montgomery march.

Lewis first entered Congress in 1986 and quickly became a figure of moral authority, with Pelosi labelling him "the conscience of the Congress."

Tributes poured in from Democrats and Republicans alike.

Senator Mitch McConnell, the chamber's Republican leader, hailed Lewis as "a pioneering civil rights leader who put his life on the line to fight racism, promote equal rights, and bring our nation into greater alignment with its founding principles."

Lewis had stepped away from his congressional duties in recent months as he underwent treatment for cancer.

But he returned to Washington in early June, in the midst of fiery demonstrations following the police killing of George Floyd in Minneapolis, to walk in Black Lives Matter Plaza, the renamed intersection near the White House that was the site of protests against injustice.